DBeaver uses SWT toolkit, its widgets are as platform-native as Java can do. Some of them can be much faster with long text editing than default Java Swing widgets.
Yup, SWT is a wrapper for actual native widgets, similar to wxWidgets. Some widgets are custom though, like the horrendously ugly tab widgets, which might be what the other commenter is reacting to. And the spacing and alignment usually doesn't look great in most SWT-based apps I've seen, for some reason.